The use of thin film coated substrates is ubiquitous in today's society. For example, thin film deposition is used for numerous aspects of consumer electronics (from integrated circuit fabrication to cell phone, computer and television display coatings), optics (e.g., coating glass), microparticle fabrication, photovoltaic fabrication, and packaging (e.g., aluminum coating on plastic for potato chip bags). In general, thin film deposition can be characterized as the deposition of a thin film, or thin layer, of material onto a substrate. Here substrate can refer to both the base material onto which the thin film is being deposited and any previously deposited layers. Thin film deposition can be split into chemical deposition and physical deposition processes.
Taking the production of solar modules or photovoltaic modules as an example, this is an area where the quality of the thin films and the expense and efficiency of producing the photovoltaic modules with the thin films are all significant in producing a commercially viable product. Numerous methods have been used for thin film deposition in photovoltaic module production, such as chemical vapor deposition (CVD) processes, including plasma-enhanced chemical vapor deposition (PECVD), and physical vapor deposition processes, including sputter deposition and evaporative deposition. While there has been significant development and improvement of thin film deposition processes for photovoltaic module production, any process can benefit from improved film uniformity, lower material waste and reduced downtime.
Taking one of these processes as an example, referring to FIG. 1 and FIG. 2 there are sectional views of an exemplary evaporative deposition system 1000 that could be used for thin film deposition during photovoltaic module production. This evaporative deposition system 1000 could be used for a closed space sublimation (CSS) or heated pocket deposition (HPD) process. The evaporative deposition system 1000 shown in FIG. 1 and FIG. 2 includes a source 1100 that contains a deposition material 1200. The source 1100 is disposed within a vacuum chamber (not shown). In FIG. 1, a substrate transport 2000 is shown which is configured to carry and position a substrate 3000 over the source 1100. FIG. 2, which is a sectional view orthogonal to that of FIG. 1, shows the substrate transport 2000 holding the sides of substrate 3000 carrying the substrate into (or out of) the paper.
In operation, the source 1100 is heated sufficiently such that the deposition material 1200 reaches a sublimation point. At the sublimation point, particles 1210 of the deposition material 1200 separate and enter a vapor pocket 1300. Optimally, the particles 1210, or vapor 1210, will travel through the vapor pocket 1300 and condense evenly across the surface of substrate 3000 forming a thin film. In order for this to occur, two conditions must occur (1) the energy of a particle 1210 must be low enough so that it does not continue to bounce off the substrate 3000; and (2) the surface temperature of the substrate 3000 must be low enough to absorb the latent heat within the particle 1210. However, numerous factors can negatively impact the quality of the thin film and the efficiency of the process.
For example, in current evaporative deposition systems 1000 the walls 1110 of the source 1100 are vertical. As a result (a) thermal energy radiated directly to the substrate 3000 heating the edges of the substrate 3000 near the walls 1110; and (b) a particle 1210 which impacted the vertical side wall would gain energy. These affects would make it less likely for a particle 1210 to deposit near the edges of the substrate 3000 resulting in the deposition of a non-uniform thin film.
In addition, it should be recognized that the substrate 3000 can deform under its own weight and/or bow due to thermal gradient through the thickness of the substrate 3000. Elevated temperatures in certain process conditions can further accentuate these problems. For purposes of illustration, this deformation is shown in exaggerated form in FIG. 1. Due to the deformation of the substrate 3000 there needs to be sufficient clearance between the substrate transport 2000 and the source 1100. However, this clearance creates a gap 1120 between the substrate 3000 and the source 1100 where particles 1210, or vapor 1210, can escape and deposit on other portions of the vacuum chamber (not shown). This causes multiple sources of inefficiency, such as material loss, increased costs for cleaning surfaces inside the vacuum chamber, and lost production time when the process is shutdown for cleaning.
Although present devices are functional, they are not sufficiently accurate or otherwise satisfactory. Accordingly, a system and method are needed to address the shortfalls of present technology and to provide other new and innovative features.